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Hello community,
Does anybody know how to get the number of elements in a structure? Is this possible in TwinCAT?
TYPE ST_Employee : STRUCT sName: STRING; nEmployeeID : INT; nAge : INT; END_STRUCT END_TYPE
For example, I want to have a function block like this :
fbCountStructElements(st := stEmployee, nElementsCount=> nStEmployeeElementCount );
nStEmployeeElementCount will be 3 after running this function block.
Thank you so much in advance!
@iotea Actually, I don't really know how this can be done using TwinCAT 3 only, but this question got me thinking and I used python to count the elements in the struct file and just published this tutorial. Hope it helps!
Counting the elements in STRUCT
@iotea yep this is possible to do.
Source code of this can be found here... https://github.com/benhar-dev/tc3-count-structure-elements
@iotea they are great answers. My question is : why do you want to know number of elements?
I think the only way this could be done is if the structure has a known format, such as a repeating number of known datatypes. In this case you could use __VARINFO to get the total bit size of the structure, then do the math. (Might be necessary to change pack_mode in struct.) If there is any way to get further information programmatically, I'd also be interested to know!
https://infosys.beckhoff.com/english.php?content=../content/1033/tc3_plc_intro/3527777675.html&id=
https://infosys.beckhoff.com/english.php?content=../content/1033/tc3_plc_intro/2529746059.html&id=
@kolyur Thank you! I also thought about doing this. However, not all the datatypes are unknown in the struct I want to use.
There was already a StackOverflow question asking the same question. I linked to the two answers from here.
You could use ADS to read the Symbol Information of that Variable and count the subitems.
See...
- "PLC_ReadSymInfoByNameEx": https://infosys.beckhoff.com/content/1033/tcplclib_tc2_utilities/35051659.html
- ADS over C++ to read variable declaration: https://infosys.beckhoff.com/content/1033/tc3_adsdll2/124832011.html
- ADS over C# to read variable declaration: https://infosys.beckhoff.com/content/1033/tc3_adssamples_net/185253899.html
@neals Thank you for the suggestions! How would you do it using the first method ? It doesn't show the subitems, but it shows the byteSize.
Have you achieved counting the subitems using the 'PLC_ReadSymInfoByNameEx' function block?
Quick tip if it helps:
{attribute 'pack_mode' := '1'}
TYPE ST_MyStruct:
STRUCT
bEnable : BOOL;
nCounter : INT;
nMaxSize : INT;
bMaxSizeReached : BOOL;
bReset : BOOL;
END_STRUCT
END_TYPE
then if you use SIZEOF(ST_MyStruct) it will give you the size/number of items you have in your structure
@raoliveira Thank you! It will give you the size of the struct, but without knowing the datatypes in the struct, you can't calculate how many items there are 🙂 @benhar-dev's solution works great! https://github.com/benhar-dev/tc3-count-structure-elements